In completing most petroleum-producing wells, it is common to provide casing throughout the wellbore and then secure the casing in place by placing cement between the casing and wellbore to fill the space therebetween. As known, the cement oftens develops voids or channels therein that, if in certain areas of the well, can lead to substantial problems in the operation the well. For example, it is not uncommon for channels to occur in the cement adjacent the perforations which are formed through the casing adjacent a producing formation to provide access for productions fluids into the casing. If such channels extend downward, water which normally underlies a hydrocarbon producing formation or zone will flow up through the channels and through the perforations to be produced with the desired fluids thereby causing high water-to-oil ratios. Since this water has to be separated and disposed of at the surface, the economics of the well can be substantially adversely affected. If such channels extend upward, gas which overlies the producing zone flows downward through the channels thereby causing high gas-to-oil ratios.
When increased water or gas production is detected and it is determined that it is being caused by channeling within the cement, it is common in the art to perform a "squeeze cement" operation to plug these channels to thereby block flow of gas or water to the production zone from the overlying or underlying zones. A typical hereto known operation for carrying out such an operation involves pulling the production tubing and any related downhole equipment from the well bore, packing off the effected interval, and pumping cement under pressure down the borehole and into the channels through the perforations. The cement is allowed to set and then a drill bit is lowered on a drill string through the casing to drill out the cement plug normally left in the casing. The casing is then re-perforated and the tubing is replaced or vice versa to complete the operation.
The above-described operation requires a work-over rig to pull and replace the tubing and to drill the cement out of the casing once it has set. While necessary, this is both expensive and time-consuming. The "tree" at the wellhead has to be "nippled down" or the well has to be disconnected from the production facilities in order for the production tubing to be pulled. The above procedure then has to be reversed after the squeeze operation has been carried out before production can be resumed thereby extending the downtime during which time the profits for production are lost.
Also, when using a rig, mud or a "kill pill" is used to maintain pressure control on high pressure wells. This mud or "kill pill" normally plugs the channels and has to be cleaned out in order to get a good squeeze job. The cleaning of the channels is extremely difficult if is can be done at all. Further, during the drilling of the cement left in the casing, the casing may be damaged by the drill bit and the vibrations in the casing caused by the drilling may loosen or redamage the cement behind the casing.